As a magnetic recording medium adapted to be mounted in a hard disk drive device (HDD device), there is a magnetic disk. The magnetic disk is produced by stacking a magnetic layer and a protective layer over a substrate in which a NiP film is coated on a metal plate made of an aluminum-magnesium alloy or the like, a glass substrate, or a ceramic substrate. Aluminum alloy substrates have conventionally been widely used as substrates for magnetic disks. However, following the reduction in size and thickness and the increase in recording density of magnetic disks in recent years, glass substrates excellent in surface flatness and thin-plate strength as compared with the aluminum alloy substrates have started to be used.
Such a magnetic disk glass substrate is manufactured through processes such as a material processing process and a first lapping process (first grinding process); an end portion shaping process (coring process for forming a hole and chamfering process for forming chamfered faces at end portions (outer peripheral end portion and inner peripheral end portion) (chamfered face forming process)); an end face polishing process (outer peripheral end portion and inner peripheral end portion); a second lapping process (second grinding process); a main surface polishing process (first and second polishing processes); and a chemical strengthening process.
The recording density of a magnetic disk has been increasing year by year and even a magnetic disk with 100 GB or more on its one side has been developed. Currently, the magnetic disk satisfies a required recording capacity as the sum on both sides thereof. However, if the recording density increases in this manner, the required recording capacity will be satisfied only on one side of a magnetic disk in the case of an electronic device that does not require a so large recording capacity. If the required recording capacity is satisfied only on one side of the magnetic disk as described above, the number of components can be reduced on the HDD device side such that a single magnetic head is provided for one magnetic disk. This is advantageous in terms of cost and further makes it possible to achieve a reduction in thickness of the HDD device. Therefore, it is expected that from now on there will be an increasing need for a magnetic disk having a magnetic layer only on one side thereof (see, e.g. JP-A-2001-351229 (Patent Document 1)).